1. Technical Field
The present invention relates to a high frequency wireless circuit apparatus mainly used in mobile communication appliances such as a portable telephone and an information communication terminal.
2. Background Art
Generally, the high frequency wireless circuit apparatus of this type has been composed as shown in FIG. 6. In the drawing, the reference numeral 11 denotes an antenna; 12 denotes a switch; 13 denotes an antenna duplexer; 14 denotes an isolator; 15 denotes a power amplifier; 16 denotes a low noise amplifier; 17 denotes a transmitting input terminal; and 18 denotes a receiving output terminal. The antenna duplexer 13 and the low noise amplifier 16 have been connected directly without any interposing means. Reference numerals 21, 22 are respectively a transmitting terminal and a receiving terminal of the antenna duplexer 13.
The transmission signal input from the transmitting input terminal 17 is amplified in the power amplifier 15, and is fed into the transmitting terminal 21 of the antenna duplexer 13 through the isolator 14. The isolator 14 is provided so that the transmission characteristic of the power amplifier 15 may not fluctuate even if the load of the antenna 11 changes. The transmission signal output from the antenna duplexer 13 is radiated into the air from the antenna 11 through the switch 12.
On the other hand, the reception signal input from the antenna 11 is fed into the antenna duplexer 13 through the switch 12, and is output into the receiving terminal 22 of the antenna duplexer 13. This reception signal is input to the low noise amplifier 16 through a phase shifter 10, and amplified, and sent out to the receiving output terminal 18.
The transmission signal fed into the antenna duplexer 13 is also sent to the receiving terminal 22 of the antenna duplexer 13. The switch 12 is not always necessary, or two or more switches may be connected to the contrary.
In such conventional structure, however, when the antenna duplexer 13 and the low noise amplifier 16 are directly connected, the transmission power amplified in the power amplifier 15 passes through the receiving terminal 22 of the antenna duplexer 13 and is mixed into the low noise amplifier 16. The transmission power amplified possibly causes cross modulation with an incoming interference signal from the antenna 11. As a result the reception sensitivity deteriorates.
In particular, this phenomenon occurs frequently in the CDMA system wireless communication, and it has been difficult to satisfy the interference wave input level of xe2x88x9230 dBm in the single wave interference characteristic determined in the standard.
That is, in the case of CDMA system wireless communication, the transmission signal output to the reception signal terminal 22 of the antenna duplexer 13 is modulated by CDMA, and has a modulation band width. On the other hand, the reception signal input through the antenna 11 is a CDMA modulated wave same as the transmission signal, but the interference signal input through the antenna 11 is a non-modulated signal. When the nonmodulated interference wave and the CDMA modulated transmission signal are fed into the low noise amplifier 16, the two-wave input distortion occurs. Then the intermodulation distortion and cross modulation distortion occurs. The CDMA modulated wave has a band. Then the wave caused by the cross modulation of interference waves and the transmission wave covers the reception signal band, thereby disabling the reception.
It is hence an object of the invention to enhance the reception sensitivity and immunity to interference signals in a high frequency wireless circuit apparatus used in mobile communication appliances such as a portable telephone and an information communication terminal.
To achieve the object, the high frequency wireless circuit apparatus of the invention is composed by connecting a phase shifter between an antenna duplexer and a low noise amplifier, so that the impedance of the receiving terminal of the antenna duplexer at a transmission frequency and the input impedance of the low noise amplifier may not be matched in complex conjugates of each other. It prevents the transmission output passing through the receiving terminal of the antenna duplexer and the interference signal entered through the antenna from causing the cross modulation in the low noise amplifier. Thus the reception sensitivity and immunity to interference signal of the high frequency wireless circuit apparatus improve at the same time.